A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In order to be able to image smaller features, it has been proposed to use extreme ultraviolet radiation (EUV) with a wavelength in the range of 5 to 20 nm, particularly 13.5 nm, or a charged particle beam, e.g. an ion beam or an electron beam, as the exposure radiation in a lithographic apparatus. An example of an EUV radiation source is a laser produced plasma source or a discharge produced plasma source. Plasma radiation sources, however, besides EUV radiation often generate debris, which debris should be kept from entering an illumination system and/or a projection lens.
International Patent Application WO 99/42904, incorporated herein by reference, discloses a debris filter including a plurality of foils or plates, which foils or plates are arranged radially around the radiation source.
European Patent Application EP 1274287 discloses a debris removing system for preventing debris emitted by a radiation source, from entering an optical system. The debris removing system includes a trapping unit having a trapping surface, e.g. a plurality of fins, (approximately) parallel to an axis passing through the radiation source. The debris removing system further includes a rotation unit for rotating the trapping unit about the axis.